This invention relates to an aerosol mass spectrometer and a method for classifying aerosol particles according to specific mass. Specific mass for the purposes of this application is defined as the ratio of particle mass to particle electric charge and is related uniquely to mass in some practically important situations. Therefore, this device and method can also be used for mass analysis of aerosol particles.
It has been known to classify aerosol particles in various types of classifiers, including a differential mobility analyzer, cascade impactor, diffusion battery, conifuge and aerosol centrifuge. All of these types of classifiers classify particles according to their electrical or mechanical mobility or diffusion coefficient, from which particle size can be deduced. None of these devices are capable of classifying particles according to specific mass and thereby to particle mass.
U.S. Pat. No. 4,383,171 describes a system for analyzing particles in aerosols, such as in air pollution studies, which enables rapid chemical analysis of particles. A controlled stream of individual particles to be analyzed is vaporized and ionized while they move in free flight, for analysis by a mass spectrometer. The air with suspended particles moves through a capillary tube for producing a stream of particles which are passed through a skimmer device having a small opening spaced from an end of the capillary tube and a vacuum pump pumps air out of the space between the tube and the skimmer while further creating an inflow of air and particles through the capillary tube. A laser beam of sufficient intensity may be used for vaporizing and ionizing the particles while in free flight passing through the skimmer opening.
U.S. Pat. No. 4,977,785 describes a method and apparatus for introducing fluid streams into mass spectrometers and other gas phase detectors by generating an aerosol during decompression of a gas, liquid or supercritical fluid stream, the aerosol's properties being dependent upon mass flow, pressure, temperature, solubility of sample, and the physical dimensions of the aerosol generating device. After the aerosol is generated, a less volatile sample in the form of condensed particles is separated from the gaseous components by accelerating the aerosol through a nozzle restrictor and utilizing momentum differences between solute particles and carrier gas molecules to obtain high solute enrichments. The apparatus functions as an interface between a supercritical fluid chromatograph and the mass spectrometer.
Other methods and apparatus for analyzing by mass spectrometry are described in U.S. Pat. Nos. 4,283,626 and 4,818,864.
U.S. Pat. No. 3,780,937 describes a centrifugal gas separator having a vertically oriented centrifuge mounted on bearings within a stationary housing and driven by an electric motor in annular form having the stator portion thereof fixed to the stationary housing and the rotor portion thereof fixed to the centrifuge drum. When energized, the magnetic attraction between the stator and rotor portions tends to lift the centrifuge drum thereby reducing the weight supported by the bearings. Elastomagnetic devices may also be provided to dampen the vibration of the rotating centrifuge drum. A mixed gas to be isotopically separated is introduced into the drum through an inlet in the housing. The lower portion of the drum is heated and the upper portion is cooled to produce a temperature gradient across the drum axially for producing positive circulation of the mixed input gas in the drum. The centrifuging and the temperature gradient produces gas separation and the gas having a relatively light molecular weight is exhausted through orifices through the lower part of the drum and heavier molecular weight gases are exhausted through orifices in the upper part of the drum. The gas to be separated is inserted through one end of the drum for separation therein.
U.S. Pat. No. 3,860,167 describes a gas sampling device for a rotating bowl centrifuge having a cylindrical shell rotated at high speed concentrically around a hollow column and chambers at opposite ends in which are located scoops having sampling orifices for collecting the gas in the respective chambers.
U.S. Pat. No. 4,182,480 describes a gas centrifuge having a centrifuge rotor mounted inside a housing and driven by an electric motor at one end thereof. Gas enters the separating space within the drum and is separated into an outer layer of liquified gas at the inner surface of the drum and helium in the natural gas in gaseous form inside the drum, the separated components being drained off through separate means.
The above prior art is incorporated herein by reference.